We evaluated the importance participants assigned to different factors by analyzing the choices they made between the flight options. Unsurprisingly, price was the strongest factor determining flight choice, even for the university travelers who reimburse themselves with grant money. However, in both studies, we found that people were willing to pay about $20 more for a flight with 100 kilograms fewer emissions than an alternative offered, even when both flights were nonstop or both included a layover.
This might not sound like a lot, but let’s compare it with the cost of carbon offsets. The flight search tradeoff of $20 per 100 kilograms translates to $200 per ton of CO2 saved, while carbon offsets cost on average $2.50 per ton in 2020. Travelers value the reduced emissions flights at 80 times the rate of traditional carbon offsets.
A good excuse to fly nonstop
Customers already balance cost against other factors when choosing a flight. For instance, it often costs more to fly direct and avoid layovers. Since carbon emissions are lower for nonstop flights, providing emissions information to consumers at the point of purchase might nudge some of them into springing for that nonstop flight. In our first study, we compared flights with layovers and direct flights, and found that our participants would pay $51 on average to avoid a layover without seeing emissions information, but $83 to do so when they see that it is also a lower-emissions flight.
The participants in our second study were our fellow employees at UC Davis, which is closest to the Sacramento airport (SMF), but which is also accessible from the much larger San Francisco International airport (SFO). Nearly half of all U.S. flights occur in such multi-airport regions, and customers have to decide whether to use their closest airport, which may not have many nonstop flights, or to avoid layovers by flying out of the more distant airport. We found that our participants were willing to pay $123 more to fly out of Sacramento instead of San Francisco for a domestic flight, all else being equal. Their willingness to pay to avoid a layover was about the same — $115 — meaning that for many, the choice between a nonstop out of San Francisco versus a layover flight out of Sacramento was indeed a toss-up. But when we highlight carbon emissions, the scale quickly tips toward the SFO nonstop flight — lower emissions break the tie and nudge the user to choose the direct flight.
Of course, how you get to the more distant airport makes a difference, both environmentally and financially. Our emissions estimates assumed that the passenger was driving a reasonably fuel-efficient car and parking at the airport, but taking public transportation at least part of the way (as many of our participants do) makes the greener option even more enticing, while having a friend drive you in a less fuel-efficient vehicle and then return to pick you up can come close to erasing the emissions savings of the more efficient flight.
Because we based our UC Davis experiment on actual employee travel, we were able to model the potential impact of using a GreenFLY-like interface for business travel costs and emissions. We estimated that UC Davis could save 79 tons of emissions, which is about 4% of employee air travel emissions — modest but significant in the context of the University of California system’s recent goal of reducing all travel emissions by 20%. We also found that these relatively modest savings would be combined with an annual $56,000 reduction in airfare costs, mostly due to the increased willingness of travelers to use nonstop flight options out of SFO, which indeed are often cheaper than layover flights from Sacramento. Depending on how employees get to the airport, this financial savings might be negated by higher ground transportation or parking costs. Even so, adding emissions information to flight searches might be a very low-cost way for large institutions to reduce travel emissions.